Electric switch



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l w. M if EGTRIG SWITCH 67 ITvew/wtov: 57 James M. Avda-EPSON,

by dq/W @wz lr-a Attorney- Patented June 4, i946 ELECTRIC SWITCH JamesM. Anderson, Broomall, Pa., assignor to General Electric Company, acorporation of New York Application December 12, 1942, SerialNo.-468,782

(Cl. 20G-89) 6 Claims.

My improvement relates to improvements in electric switches and moreparticularly high speed circuit breakers and especially high speedautomatic trip-free circuit breakers having a plurality of poles, whichare independent of each other with respect to their circuit openingoperation, and have a single operating mechanism for simultaneouslyactuating to the closed circuit position all poles fully open at anytime.

Probably the greatest trouble experienced in the operation of mercuryarc rectiers arises from abnormal operating conditions such as anarc-back occasioned by reverse current iiow from cathode to anode or bythe striking of an arc discharge between anodes. The reversal of currentflow establishes a short circuit which is fed not only by the otherrectifying paths of the particular rectier, but also by all the rectiersoperating in parallel with this rectifier. The rate of increase ofcurrent in this short circuit path is so high, particularly in largeinstallations, that currents dangerous to equipment and personnel anddestructive of service continuity are quickly reached. There have beenobserved rates of increase of current of over six million amperes asecond for a single rectier and over eleven million amperes a secondwhere several are operated in parallel. It is, therefore, imperative tointerrupt this short -circuit current very quickly if the current atinterruption is not to exceed a safe value and interruption of serviceis to be prevented. In short, the problem is to interrupt the circuit ofthe faulty anode so quickly as to limit the resulting current to a safevalue. But parts such as the movable contact of the circuit breaker andassociated members mechanically actuated fast enough to accomplish suchquick circuit interruption must also be stopped quickly.

Also, the movement of such parts may be highly accelerated by magneticforces due to the short circuit current being opened. The natural resultis for these parts to rebound to the extent even that they may reclosethe circuit and thereby reestablish the fault arc. This would bedangerous to both personnel and equipment. Buffers with a slowing orsnubbing action sufiicient to prevent serious rebound introduce spaceand time features which render them more or less impractical from thestandpoint of space, performance, and cost considerations. Moreover,where a relatively small quick opening movement is important, the use ofbuiers to prevent rebound is not satisfactory since they would require aslowing down of the moving parts before the contact gap was sufficientto insure the interruption of the fault arc.

An object of my invention is to provide, for circuit breakers andparticularly high speed circuit breakers, an improved arrangement forpreventing, at the time of the circuit opening operation, anysubstantial rebound of the movable Contact and the parts associatedtherewith. Another object of my invention is to provide an improvedanti-rebound arrangement which is applicable Vto either single ypole ormultipole circuit breakers and particularly multipole circuit breakerswhose poles are independent of each other with respect to their circuitopening operation but which have a single closing mechanism forsimultaneously closing all poles that are open at any time. A furtherobject of my invention is to provide an improved positive anti-reboundarrangement whose holding action is automatically released during theresetting operation of the circuit breaker mechanism. A still furtherobject of my invention is to provide an improved antirebound arrangementwhich is relatively simple and inexpensive. These and other objects ofmy invention will hereinafter appear in more detail.

In accordance with my invention, I provide, for circuit breakers, animproved -anti-rebound arrangement comprising two cooperating elementswhich are operative to engage each other near the end of the circuitopening movement of the movable contact and by such engagement to holdthe contact against appreciable movement toward the circuit closingposition. A.lso in accordance with my invention, I so arrange thesecooperating elements thati one has a stationary mounting and the otheris mounted for movement with the movable contact o the circuit breaker.Further in accordance with my invention, I provide means forautomatically releasing the .anti-rebound or holding action of thesecooperating elements during the resetting operation of the circuitbreaker mechanism.

My invention will be better understood from the following descriptionwhen considered in connection with the accompanying two sheets ofdrawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings, Fig. l is a side elevation, partly brokenaway and partly in section, `of a high speed automatic trip-free circuitbreaker, shown in the closed position and embodying my invention; Fig. 2is `a view similar to Fig. lshowing the position oi the parts near theend of the circuit opening movement with the anti-rebound effect inaction; Fig. 3 is a view similar to Fig. 2 showing the circuit breakerparts in the full open position with the resetting action completedpreparatory to closing the circuit breaker and with the anti-reboundmechanism also reset; Fig. 4 is a front elevation, to an enlarged scale,partly in section of a portion of the circuit breaker mechanismillustrating my antirebound arrangement in more detail; and Fig. 5 is afront elevation in outline of a multipole circuit breaker having aplurality of pole elements like that shown in Figs. 1, 2 and 3, eachprovided with anti-rebound means embodying my invention.

In thc single pole circuit breaker 6 shown in Figs. 1, 2 and 3 for thepurpose of illustrating my invention, a base or panel I of suitableinsulating material has suitably secured thereto spaced lower and uppercontact studs I and I2, respectively, which are provided with terminalsI3 and I4, respectively. The stud I I comprises a stationary contactblock I having a curved contacting surface I6, which, as shown, iscylindrical. The stud I2 comprises a contact block I1 in which issupported a plurality of relatively stationary contacts I8, only one ofwhich appears in the drawing. Each oi' such contacts I8 is arranged forhigh pressure line contact with the stud block I1. For this purpose,each contact I8 is mounted with its upper end fitting somewhat looselyin a cylindrical recess I9 in the stud block I1. As shown more clearlyin Fig. 1, the mounting for each contact I8 includes a headed screw 20and a backing spring 2|. The screw is supported in an opening in thestud I2 and screwed into the block I1. In order to maintain a sharpcurrent loop at the contact recess I9, the head of the screw 20 iscentered in the opening of the stud I2 by an insulating bushing, notshown. This prevents the passage of current from the block l1 throughthe screw 20 and the spring 2| to the stud I2. The spring 2| between thehead of the screw 2|) and the contact I8 provides a bias to hold theupper end 22 of the contact I8 forward against the face of the recess I9in line-to-line contact. For better contact action, the upper end of thecontact I8 and the surface of the recess I9 against which it bears issilver faced. Likewise, the lower end of the contact I8 is provided witha silver contact piece 23.

For completing a circuit through the circuit breaker, there is provideda contact 24, the plane surface 25 of which is fulcrumed on thecylindrical contacting surface I6 of the stationary contact I5 formovement into engagement with the relatively stationary contact I8 by amechanism so constructed as to insure high speed circuit opening action.In the arrangement illustrated, the lower end of the contact 24 isprovided with a plane contact surface 25 which bears on the cylindricalcontact surface |8 of the contact block I5. Both of the contact surfacesIB and 25 are silver faced for better contact action. At an intermediatepoint in its length, the movable contact 24 is provided with a silvercontact portion 26, which is arranged to engage the silver portion 23 oneach of the contacts I8. The contacts I8 are spaced slightly byseparators 21 in order that each may be free to move independently ofthe others under the magnetic attracting forces between them due to thecurrents flowing through them in the same direction and thus come to abetter bearing in the contact recess |9 and against the contact face 26of the movable contact 24. 'I'he separators are preferably notofmagnetic material but suitable insulating material may be used. Inaddition to the primary stationary contacts I8 there is also provided asecondary or arcing stationary contact 28 whose upper end is mounted ina cy1indrical recess 29 in an arcing contact block 30 separated from thecontact block l1 by suitable insulation. Like the primary stationarycontacts I8, the secondary stationary contact 28 is biased forward toengage the arcing contact block 3D in line-to-line contact. For thispurpose, there is provided one or more backing springs 3|, which aremounted in holes in the stud I2. The backing springs 3| do not engagethe contact 28 directly but are spaced therefrom by insulating rods 32.The lower end oi1 the secondary stationary contact 2B and the upper endoi' the movable contact 24 are provided with suitable contact portions33.

For arc extinguishing purposes, the arcing contact block 353 is providedwith au arcing horn extension 34 and is, also, connected to the stud I2through a blowout coil 35. For carrying the end of the arc oil" from thecontact portion 33 of the movable contact 24, there may be provided, aswill be obvious to those skilled in the art, a blowout coil connectedbetween an arcing horn, not shown, and the lower stud II of the circuitbreaker, The arc extinguishing structure further includes two enclosingbarriers 36, only one of which is partially shown in the drawings.

In order that the plane face 25 of the movable bridging contact 24 maypivot on the cylindrical face I8 of the contact block I5, the contact 24is mounted on suitable supporting means, such as a cradle 31. pivoted torotate about an axis which is substantially in line with the element ofthe cylindrical surface I6 about which the contact pivots as a linecontact. In other Words, the construction is such that the pivotal axesof the Contact 24 and the cradle are as nearly coincident as possible inorder to reduce the sliding between and consequent wear of the contactsurfaces I6 and 25 to a minimum. As shown, this cradle comprises twospaced side members 31, only one of which appears in the drawings. Eachof these is supported on a pivot 38 mounted in the side 39 of thecircuit breaker frame adjacent the side member of the cradle. At theupper end, the side members 31 are joined by a pivot 4|), which passesthrough the contact 24 and leaves this contact free to be biased againstthe contact surface and for high speed of opening operation. It will benoted that in the circuit closed position of the Contact structuredescribed, the magnetic loop expansion effect produced by any currentthrough the circuit breaker increases the pressure between the contactsas long as the cradle 31 is maintained in the closed circuit positionand, consequently, tends to accelerate contact separation when thecradle is free to rotate clockwise about its pivots 33.

In order to move the cradle 31 into and maintain it in the closedcircuit position and yet have it quickly freed for high speedinterruption, there is provided'a movable abutment 4|, releasable meanscomprising a latch 42 pivoted in the frame 39 at 43 for holding theabutment 4| in a predetermined position, and actuating means comprisinga member 44 movable on the abutment 4I and between the abutment and amember 45 movable with the bridging contact 24, for example, pivoted onthe cradle 31. In order to minimize friction and facilitate high speedoperation, the members 44 and 45 are preferably rollers, as shown. Theabutment 4| is mounted on a pivot 4B extending between the sides 39 ofthe circuit breaker frame. Inl order tofobtain the counter clockwisemovement of the cradle 31 necessary tobring the contact 24 into thenormal current.v

conducting position, the abutment 4I is provided with a suitably shapedcam face 41, which is traversed by the roller 44. For actuating theroller 44, there is provided. an operating member 48 which, as shownpismounted on the pivot 46 and is connected tothe roller 44 throughone ormore operating links r49.- These links are pivoted to theoperating-member 48 at 50 and to the roller 44 at 5l. The operatingmember comprises two side pieces 48 and a cross connectionv 52, which inthe closed position of. the circuit breaker abuts the frame 39 at 53, asshown inFig. 1. In order to maintainthe circuitl breaker in this closedposition as long as the abutment 4l is maintained in the latchedpositionthe parts are so proportioned and arranged thatinthe closedposition of the circuit breaker thel directionof pressure on the rollervv44 tends to force this roller to the right on the cam sury face41 soas t provide the. necessary holding.'

bias. ,Y

Forreleasing .thelatch 42 so as to eiiect the opening ofthe circuitbreaker, there is provided electromagnetic means responsive to apredetermined abnormal condition of the circuit con-- trolled.bytheicircuit breaker. The particular meansillustrated is responsive toa predetermined direction of flow of direct current. As shown, thismeans comprises two U-shaped cores 54 and 55 of suitable magneticmaterial. The core 54 has. leg portions 540 and 54| which areinterconnected by a cross portion 542. Only one of the leg por tions 550of the core 55 appears in the drawings. These leg portions areinterconnected by ay crossI portion 552 which appears in Fig, 1. Thecores 54 and 55 are arranged substantially perpendicularly to each otherand have two common polar extensions 55, only one of which appears inthe drawings, with an air gap arranged to be bridged byan armature 51.The core 54 issecuredto the frame v,39 so as to embrace thestud il andis accordingly energized responsively to the magnitude and direction ofthe current nowing through the circuit breaker. The core 55 is energizedby polarizing windings 58 only one of which appears in. the drawings.one on each leg ,of the magnet and energized preferably from a source ofdirect potential although rectiiied alternating current may be used.I'I'he flux of these polarizing windings alone is suincient to maintainthe armature 51 in the attracted position against thebias. of a latchactuatingspring 59, which pushes against the tail of thelatch 42 througha collared rod 50 passing through the armature 51. A turned down portionv.of the rod 60 passes through the armature 51., the shoulder on the rodwhere the diameter is reduced ,being employed to move the armatureA 51away from the magnet pole faces because of the bias-of ,the spring 59 onthe occasions of predetermlned current conditions in the breaker. Themagnetic structure and arrangement is such that when current flowsthrough the circuit breaker ina predetermined direction the iiuX due tothe current is additive in its effect to the. armature holding eiect ofthe flux due to the windings 58. However, lwhencurrent iiows through thecircuitl breaker in a direction opposite to lsaidpredeterfY mineddirection, the two fluxes not only are subs tractive intheirresultantholding eiect, but also are. so shifted that thearmature 51 is`quickly re-.- leased to: trip the latcnf42 understheractionizof...

These windings are arranged `the abutment clockwise about its pivot 46.

the spring. 59.: -Thebiasof the springmay. be

controlled by 'a nut' 6l: threaded `on a spring sup: port 62, whichlmayalso serve to secure the re-i movable bottomn of thev U -shaped magneticstruc.-

the circuit breaker.

the attracted position during the opening of the circuit breaker', IVprovide means responsive to the movement of theabutment 4I. As shown,this means comprises a link 63 pivoted at 64 to the A.tensions 56. Theplug 68, screwed into the frame,

provides a shoulderstop for the armature51. so that the armature vcannot compress the spring 61 to its solidv height as the armaturemovesfand thereby strip the collar 69 secured to the rod 60 l therefrom.For'. resetting the'abutment 4I and the latch 42 to the sustainingposition, I provider abutment return springs .10 and a latch returnspring 1l. The former is secured to the abutment pivot 64and to theframe l39 and tends to turn latch return spring -ll isrconnected betweenthe latch 42 and the frame 39 and tends to turn the l latch clockwiseabout its pivot 43. f

For effecting a quick movement of the contact 24 to the open circuitposition,.exerting pressure between the contact surfaces it and 25 atall times, and also recornpressing the tripping spring 55, there isyprovided` suitable .energy storing means, suchv as biasing springs 12,only one of which appears inthe drawing. These `springs are positionedoutside of the cradle 31. ln order to have them suitablyv stresseddui-ing the clos-v ingA movement of the breaker, they are connectedbetween a'stud 13 supported in the sides of the frame 35 and a rod 14fixed in theV movable contact 24 but extending through slotted openings,not shown, in the cradle sides 31 so as to permit a predeterminedmovement of the contact 24 relatively to the cradle .31. .For exertingpressure between the contact surfaces I6 and25 at all times and alsoreturning the operating member 48 and the parts connected thereto to theposition shown in Fig. 3, there is provided suitable energy storingmeans, such as a biasing spring 15. In order to have this springsuitably stressed during the closing movement of the circuit breaker, itis connected between the pivot 55 and a rod 15 xed in the contact 24which is provided with a hollow portion for receiving the end of thespring.

Since mercury arc rectifiers usually have six anode circuits andsometimes more, the illustrated circuit arrangement is 'such that apluralityr or single-pole circuit breakers in the open circuit positioncan be closed simultaneously, andalso any one or morepoles can open andcan be closed Without interfering `with the poles that are closed'whereby to avoid unnecessaryinterruptions inf soundanodecircuits. Forthis-purpose, each` pole:- Ais provided.; .with :an .actuating:,flever.; 1 1 :pivotanty For resetting or returning the armature 51 toThe at 48 and these levers are interconnected by a common actuatingmeans comprising a crossbar 18. As shown, the actuating lever 11 isU-shaped with a cross piece 19 having a projection 88 arranged to abutthe cross piece 52 of the operating crank 48. In order to insure thateach pole will be positively closed, the projection 88 is adjustablypositioned so as to take care of manufacturing tolerances and variationsin lost motion whereby to insure the desired closing action of any oneor more poles even though the others are closed. The projection 88 is soadjusted that a predetermined clockwise movement of the actuating lever11 will impart suilicient clockwise movement to the operating crank 48to effect the holding bias of the rollers. This, in general, will causethe operating crank 48 to settle with its cross piece 82 abutting theframe 39 at ."3` with some clearance between the projection 88 and thecross piece 52. However, it is possible that the nal holding biasedposition of the crank 48 may be reached at the end oi the clockwisemovement of the actuating lever 11. In this case, the projection 88 maycontinue to abut the operatingr crank cross piece 52.

For actuating the crossbar 18 to ellect the resetting of the releasablemeans comprising the abutment 4| and the latch 42 and reclosing allpoles open at any time, the crossbar 18 is actuated flrstcounterclockwise and then clockwise about its pivot 46. As will beapparent to those skilled in the art, this actuation may be performedeither by manually operated mechanism or by motive power mechanism orboth suitably connected to an operating rod 8| which, as shown, ispivotally connected to a crank 82 secured to the crossbar '|8.

Because of the relatively small mass of the moving parts, the fastoperation of the tripping mechanism and the strong opening bias on themovable contact 24, it will be apparent that this contact moves to thecircuit opening position very fast. In order to prevent any tendency forthis contact to rebound in the closing direction enough to reestablishan arc, I provide, in accordance with my invention, two cooperatingelements 83. 84 which are operative to engage each other near the end ofthe circuit opening operation and thereby to hold the contact 24 againstany substantial movement in the circuit closing direction. As shown,these elements are cooperating latching devices and, in accordance withmy invention, one of the elements is in the form of a latch 83 which ismounted to partake of the movement of the contact 24. For this purpose,the latch 83 may be pivotally supported on a reduced diameter of the hubof the roller 45, as more clearly shown in Fig. 4. The other element' isin thel form of a projection or catch 84 which, in accordance with myinvention, has a stationary mounting. For this purpose, it may bemounted, as shown more clearly in Fig. 4, on the side of the circuitbreaker frame 39 or as a part of a support 85 which is rigidly securedto this frame by suitable means, comprising, as shown, cap screws 88 and86 and lock washers 81. The latch 83 is provided with a hook portion 88which is arranged to engage the catch 84 as the movable contact 24 movesto the circuit open position. For this purpose. the latch 83 is biasedfor counterclockwise rotation by suitable means such as a spring 88which extends between the latch and an arm 90 on the actuating lever 11.This spring 88 maintains the tail 8| o! the latch 83 in abuttingengagement against the stationary projection 84 while the circuitbreaker is closed and biases the hook portion 88 into interlockingengagement lwith this projection near the end of the circuit openingmovement of the contact 24 so as to prevent any material reboundthereof. In order better to guide the latch 83 in its plane o! rotation,the projection 84 may be provided with shoulder portions 92 as shown inFig. 4.

Since the latch or hook element 83 positively holds the movable contact24 in the open circuit position in consequence of its engagement withthe catch 84, it is necessary to disengage these latching elementsbefore the circuit closing operation can be effected. In order to effectthis disengagement, I provide, in accordance with my invention, meansfor releasing the latch' 83 from the catch 84 during the resettingoperation of the circuit breaker tripping and holding mechanism. Asshown, this means comprises a projection or pin 93 which is mounted onthe latch resetting links 63 in the path of movement of the tail 9| ofthe latch 83 when it is in the holding position. Consequently, duringthe resetting operation when the links 83 move from right to left underthe bias to which they are subjected, the latch 83 is turned clockwiseout of engagement with the catch 84 and positively held out of suchensagement during the closing operation of the circuit breaker. When thecircuit breaker is closed, then the tail 9| of the latch 83 abuts thecatch 84.

Assuming the circuit breaker closed with the parts positioned as shownin Fig. l and current flowing through the circuit breaker in thedirection which causes the flux of the electromagnet 55 to assist theflux of the polarizing electromagnet 56 to hold the armature 51 in theattracted position against the bias of the tripping spring 59, then, ifthe direction of the current ilowing through the circuit breaker isreversed as in the case of an arc-back in the anode circuit of a mercuryarc rectifier, the armature is quickly released because of iluxopposition and shift in the common magnetic path including the air gapbridged by the armature. The effect of the strong tripping spring 59 isto move the latch 42 forcibly counterclockwise about its pivot 43 thusreleasing the abutment 4|. Since there is no longer any support for theleft-hand or free end of the abutment 4|, the tension of the openingsprings 12 and to a certain extent, the springs 15 and the contactsprings 2| and 3| together with the weight of the parts bearing on theabutment 4| forces this member to turn in a counterclockwise directionabout its pivot 46 whereby quickly to effect the opening of the circuitbreaker with the parts positioned as shown in Fig. 2.

During this opening movement, the latch 83 moves downwardly inconsequence of the clockwise rotation oi' its pivotal support about thepivot 38. Accordingly, the tail 9| of the latch is below the catch 84and therefore, under the bias of the spring 89, the latch 83 is turnedcounterclockwise with its hook 88 under the catch 84. The movablesupport 31 of the Contact 24 is consequently positively held in the opencircuit position so that no rebound of this contact, except the veryslight amount resulting from th'e necessity for mechanical clearances,can occur. In the holding position, the tail 9| of the latch 83 ispositioned in the path of movement of the projection 93 on the resettinglinks 63.

In the position shown in Fig. 2, the bias on the roller 44, which wasaway from the panel I8, that is, in a direction to hold the circuitbreaker closed, is now directed toward the panel. If, after the openingof the circuit breaker, the crank 82 is rotated counterclockwise aboutits pivot, as by an upward movement of the operating rod 8l, then th'ecrossbar 78 is raised to the position shown in Fig. 3 with the actuatinglever T1 turning counterclockwise about its pivot 46A While this motionis going on, the remaining tension on the spring l turns the operatingcrank 4.8 counterclockwise about its pivot 46 so that the roller 44under its bias toward the panel moves to its lowest position on the camsurface 41 of the abutment 4I. During this movement, the abutment 4I andits sustaining latch 42 are returned to the latching position under thebiasing actions of their respective springs l0 and 1l. As the links E3move from right to left under the bias of the springs 1, the projection93 on one of the links engages the tail 9| of the latch 83 and turnsthis element clockwise suiilciently to have its hook 88 clear theprojection 84 and maintains this clearance until the circuit breaker isclosed. In other words, the circuit breaker mechanism is reset as shownin Fig. 3 and ready for the actual closing movement to the positionshown in Fig. 1. This is accomplished by a downward pull on the rod Eleither manually or otherwise as desired. This downward movement of theoperating rod 8i turns the actuating crank 'il' clockwise about itspivot 45. With this movement of the actuating crank, the projection 80engages the transverse portion 52 of the operating crank 48 to rotatethis member clockwise about its pivot 4E. As this motion takes place,the roller 44 travels along the cam surface 47 in contact with theroller 45 to force the cradle 3l' to turn counterclockwise about itspivot 35 and thereby to effect the engagement of the contact 24 with thecontacts I3 and 28. During this movement, the springs 12 and 'I5 arestressed in preparation for the next opening action and also to maintainthe desired contact pressure between the contact surfaces I6 and 25. Theparts are then again in the circuit closing position shown in Fig. 1.

When a plurality of circuit breaker poles 6 are under the control of thecrossbar 13, as shown in Fig. 5, each pole that may open automaticallyduring movement of the crossbar will be closed by the downward movementthereof provided the self-resetting mechanism of the opened pole canmove from the position shown in Fig. 2 to the reset position shown inFig. 3 before the movement of the crossbar has proceeded so far as toprevent such resetting action.

Furthermore, assuming a plurality of poles, each pro-vided with its ownanti-rebound arrangement embodying my invention, it will be noted thatthe movable contact 24 of any pole, which opens during the downward orclosing movement of the actuating rod 8| to close one or more otherpoles, will be held by its respective latching elements long enough toprevent rebound regardless of the position of the actuating lever 11.

It will be noted that the time during which the anti-rebound members 83and 84 are in locking engagement depends on the position of theactuating lever 17 at the time a pole opens. The minimum time will, ofcourse, occur when the actuating lever 11 is near the upper or resettingposition shown in Fig. 3 during the reclosing action of some openedpole. If at this time another pole opens, the duration of theanti-rebound action in this last opened pole is the minimiun and isdetermined by the time necessary for the operating crank 48 and theparts attached thereto and movable therewith and, also, the abutment 4land the resetting links 63 to move under the bias of springs 'I5 and 10,respectively, from the position shown in Fig. 2 to the reset positionshown in Fig. 3. It will be apparent that, since the cooperatinglatching element 84 for each pole has a stationary mounting and istherefore unaffected by any' movement of the parts of other poles or theoperating mechanism itself, the anti-rebound or latching movement of theindividual latch 83 of each pole is independent of the mechanism of theother poles.

While I have shown and described my invention in considerable detail, Ido not desire to be limited to the exact arrangements shown, but seek tocover in the appended claims all those modifications that fall withinthe true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A circuit breaker comprising a movable circuit controlling memberbiased to the open circuit position, means for holding said member inthe closed circuit position, means for effecting the release of saidholding means, and means for preventing rebound oi said member from itsopen circuit position comprising two cooperating engaging elements, onebeing stationary and the other mounted to move simultaneously with saidmember and having a tail portion arranged to abut said one element Whensaid member is in the closed circuit position and a catch portionarranged for interlocking engagement with said one element near the endof the circuit opening movement of the member, and resilient meansbiasing said other element into said abutting and interlockingengagements.

2. An electric switch comprising a movable circuit controlling memberbiased to the open circuit position, a self-resetting collapsiblemechanism for maintaining said member in the closed circuit positioncomprising a movable abutment and a link pivotally supported thereon,means for effecting the collapse of said mechanism, and means forpreventing rebound of said member from its open circuit positioncomprising a stationary element and a catch mounted to movesimultaneously with said member, said catch havingr a tail portionarranged to abut said element when said member is in the closed circuitposition and a hook portion adapted to interlock with said element nearthe end of the circuit opening movement of the member, resilient meansb-iasing said catch into said abutting and interlocking engagements, andmeans on said link engageable with the tail portion of said catch at thebeginning of the resetting movement of said collapisible mechanism tomove the catch from interlocking engagement with said element toabutting engagement therewith.

3. An electric switch comprising two cooperating contacts, trip-freemechanism for effecting relative movement oi said contacts comprising apivoted support for one of the contacts, a rst roller mounted on saidsupport, an abutment having a surface of a predetermined contour,releasable means for holding said abutment in a predetermined position,a second roller movable in one direction over the surface of saidabutment between the abutment and said iirst roller to effect thecircuit closing engagement of said contacts when the abutment is held insaid predetermined position, means for eiecting the release of saidholding means whereby to cause the circuit opening movement oi. said onecontact, means for preventing rebound of said one contact from its opencircuit position comprising a catch pivotally mounted on said pivotedsupport and a stationary element engageable by said catch near the endof the circuit opening movement of said one contact.

4. An electric switch comprising two cooperating contacts, trip-freemechanism for effecting relative movement of said contacts comprising apivoted support for one o! the contacts, a rst roller mounted on saidsupport, an abutment having a surface of a predetermined contour,releasable means for holding said abutment in a predetermined position,a second roller movable in one direction over the surface of saidabutment between the abutment and said first roller to effect thecircuit closing engagement of said contacts when the abutment is held insaid predetermined position, means for effecting the release f saidholding means whereby to cause the circuit opening movement of said onecontact, means for preventing rebound of said one contact from its opencircuit position comprising a catch pivotally mounted on said pivotedsupport and a stationary element engageable by said catch near the endof the circuit opening movement of said one contact. and means operableupon movement of said second roller over said surface in the reversedirection to move said catch out of engagement with said stationaryelement.

5. An electric switch comprising two cooperating contacts, trip-freemechanism for effecting relative movement of said contacts comprising apivoted support for one of the contacts, a first roller mounted on saidsupport, an abutment having a surface of a predetermined contour,releasable means for holding said abutment in a predetermined position,a second roller movable in one direction over the surface of saidabutment between the abutment and said first roller to effect thecircuit closing engagement of said contacts when the abutment is held insaid predetermined position, means for effecting the release of saidholding means whereby to cause the circuit opening movement of said onecontact, means for preventing rebound of said one contact from its opencircuit position comprising a catch pivotally mounted on said pivotedsupport and a stationary element engageable by said catch near the endof the circuit opening movement of said one contact, and means operableupon movement of said second roller over said surface in the reversedirection to move said catch out of engagement with said stationaryelement and to reset said releasable means to the holding position.

6. A circuit breaker comprising a Contact, a pivoted support on whichsaid contact is pivotallv mounted, means biasing said support formovement in a direction to effect the circuit opening movement of saidcontact, means for holding said support to maintain said contact in theclosed circuit position, means for effecting the releasing of saidholding means, and means for preventing rebound oi said support andcontact from the open circuit position comprising two cooperatingelements, one being mounted stationary and the other mounted on saidsupport to move simultaneously therewith and having a tail portionadapted to abut said one element when the contact is in the closedcircuit position and a catch portion adapted to interlock with said oneelement near the end oi the circuit opening movement of said memberY andresilient means for biasing said other element into said abutting andinterlocking engagements.

JAMES M. ANDERSON.

